Mitochondria is responsible for detoxification of foreign substances in mammalian liver. Most lipid soluble drugs are converted by cytochrome P450 into water-soluble metabolites, which are more easily excreted. Cytochrome P450 is a family of enzymes, which occur in the endoplasmic reticulum of cells particularly those of the liver and gastrointestinal tract. They catalyze an oxygenase reaction in which molecular oxygen is split so that one atom is used to form the hydroxylated product and the other is reduced to form water. NAPDH provides the reducing power via a series of electron carriers such as NADPH cytochrome P450 reductase.